Catodontherium Temporal range: | |
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Catodontherium fallax jaw fragment, Natural History Museum of Basel | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Artiodactyla |
Family: | † Anoplotheriidae |
Subfamily: | † Dacrytheriinae |
Genus: | † Catodontherium Depéret, 1908 |
Type species | |
†Catodus robiacensis (= †Catodontherium robiacense) Depéret, 1906 | |
Other species | |
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Synonyms | |
Genus synonymy
Synonyms of C. robiacense
Synonyms of C. fallax
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Catodontherium is an extinct genus of Palaeogene artiodactyls belonging to the family Anoplotheriidae. It was endemic to Western Europe and had a temporal range exclusive to the middle Eocene, although its earliest appearance depends on whether C. argentonicum is truly a species of Catodontherium. It was first named Catodus by the French palaeontologist Charles Depéret in 1906, who created two species for the genus and later changed the genus name to Catodontherium in 1908. The Swiss palaeontologist Hans Georg Stehlin renamed one species and classified two other newly erected species to Catodontherium in 1910. Today, there are four known species, although two remain questionable in genus placement.
Similar to the other dacrytheriine Dacrytherium and unlike anoplotheriines such as Anoplotherium , Catodontherium had a preorbital fossa. It also had cranial and dental morphologies typical of the Dacrytheriinae but had specific differences from Dacrytherium such as the position of the infraorbital foramen and forms of the premolars and molars. The anoplotheriid is known by very few facial and limb remains, most of which are fragmentary.
Typical of anoplotheriids, Catodontherium lived in Western Europe back when it was an archipelago that was isolated from the rest of Eurasia, meaning that it lived in subtropical-tropical environments with various other faunal assembagess that also evolved with high levels of endemism.
In 1906, the French palaeontologist Charles Depéret wrote about fauna groups classified as being of the Bartonian stage of the middle Eocene. According to him, the localities of Robiac in France and Mormont in Switzerland have abundant fossil remains of anthracotheres with molars lower in shape than those of the Oligocene-aged Brachyodus . He said that specimens were previously designated by François Jules Pictet de la Rive under the species name "Hyopotamus gresslyi" (previously named by Ludwig Rütimeyer in 1862) but that he could not reuse the species name because Christian Erich Hermann von Meyer applied it previously to a lost molar holotype in the form of the now-invalid species name "Tapinodon gresslyi" in 1846. Since he determined that it did not belong to "Hyopotamus" (= Bothriodon ), he decided to erect the genus name Catodus and create the species Catodus robiacensis, thinking that it may have been within the ancestral lineage of Brachyodus. He also said that Rütimeyer designated fossils of another species to Hyopotamus gresslyi, replacing it with another species name Catodus Rutimeyeri. [1] [2]
In 1908, Depéret replaced the previous genus name Catodus with the newer genus name Catodontherium but reinforced the validity of its two species. He stated that it was oldest of the Brachyodus branch, C. Rutimeyeri being the oldest known species. [3] According to the American palaeontologist George Gaylord Simpson in 1945, the genus was renamed because of apparent preoccupation of a prior genus name Catodon. He stated that the genus name was not a preoccupation but that it was a nomen nudum anyways, meaning that Catodontherium could be retained. [4]
"Hyopotamus gresslyi" was taxonomically problematic since fossils of other artiodactyls like Catodontherium and later Dacrytherium were historically assigned to it. Swiss palaeontologist Hans Georg Stehlin previously synonymized Tapinodon gresslyi and Hyopotamus gresslyi with the newly erected species Haplobunodon lydekkeri (replacing Haplobunodon picteti) in 1908. In 1910, Stehlin validated Catodontherium because its dentition differed from typical Oligocene anthracotheres by its extreme brachydonty (low crowns) and elongated premolars. He stated that the brachydonty was more extreme compared to Dacrytherium and Leptotheridium and argued that while the species name Dichodon valdense could replace C. robiacense, the former may not have been valid compared to the latter. He also created another species C. fallax and said that the other name C. rutimeyeri should be synonymized with it because it was diagnosed only on isolated teeth. He also established three additional species named C. buxgovianum, C(?) paquieri, and C(?) argentonicum based on other remains. [5] [6]
C. robiacense and C. buxgovianum have since been defined as valid species belonging to Catodontherium while C. paquieri? and C. argentonicum? remain uncertain in genus placement. The genus is described as being not as well-known compared to Dacrytherium. [7] [8]
Catodontherium belongs to the subfamily Dacrytheriinae, which belongs to the Palaeogene artiodactyl family Anoplotheriidae. [8] The family was endemic to Western Europe and lived from the middle Eocene to the early Oligocene (~44 to 30 Ma, possible earliest record at ~48 Ma). The exact evolutionary origins and dispersals of the anoplotheriids are uncertain, but they exclusively resided within the continent when it was an archipelago that was isolated by seaway barriers from other regions such as Balkanatolia and the rest of eastern Eurasia. The Anoplotheriidae's relations with other members of the Artiodactyla are not well-resolved, with some determining it to be either a tylopod (which includes camelids and merycoidodonts of the Palaeogene) or a close relative to the infraorder and some others believing that it may have been closer to the Ruminantia (which includes tragulids and other close Palaeogene relatives). [9] [10]
The history of dacrytheriines has been contentious as a result of disagreements as to whether they constitute a subfamily of the Anoplotheriidae or a distinct family named "Dacrytheriidae". The family name was first proposed by Charles Depéret in 1917 and was generally followed for decades by other palaeontologists like Jean Sudre. Since 2007, however, they were redefined as a subfamily within the Anoplotheriidae, supported by recent phylogenetic analyses determining that Dacrytherium falls within the Anoplotheriidae. It is one of two subfamilies of the Anoplotheriidae, the other being the Anoplotheriinae. [8] [11] [12]
The Dacrytheriinae is the older anoplotheriid subfamily, but the actual first appearance by Mammal Palaeogene range is uncertain. The first undisputed appearance of anoplotheriids is by MP13, but their range may have extended, in the case of Catodontherium, into MP11 or even MP10. [8] [13] Dacrytherium itself made its first undisputed appearance by MP13 as an artiodactyl leaning towards bunoselenodont (bunodont (rounded cusps) plus selenodont (crescent-shaped ridge form)) dentition. [14] The younger subfamily Anoplotheriinae made their first appearances by the late Eocene (MP15-MP16), or ~41-40 Ma, within Western Europe with Duerotherium and Robiatherium . After a significant gap of anoplotheriines in MP17a-MP17b, the derived anoplotheriids Anoplotherium and Diplobune made their first appearances in Western Europe by MP18, although their exact origins are unknown. [15] In 2022 it was suggested that Dacrytheriinae is a paraphyletic subfamily based on dental morphology from which the Anoplotheriinae, Mixtotheriidae, and Cainotherioidea stemmed, but further research is required to confirm if this is true. [16]
Conducting studies focused on the phylogenetic relations within the Anoplotheriidae has proven difficult due to the general scarcity of fossils for most of the species. [15] The phylogenetic relations of the Anoplotheriidae as well as the Xiphodontidae, Mixtotheriidae, and Cainotheriidae have also been elusive due to the selenodont morphologies of the molars, which were convergent with tylopods or ruminants. [16] Some researchers considered the selenodont families Anoplotheriidae, Xiphodontidae, and Cainotheriidae to be within Tylopoda due to postcranial features that were similar to the tylopods from North America in the Palaeogene. [17] Other researchers tie them as being more closely related to ruminants than tylopods based on dental morphology. Different phylogenetic analyses have produced different results for the "derived" selenodont Eocene European artiodactyl families, making it uncertain whether they were closer to the Tylopoda or Ruminantia. [12] [18]
In an article published in 2019, Romain Weppe et al. conducted a phylogenetic analysis on the Cainotherioidea within the Artiodactyla based on mandibular and dental characteristics, specifically in terms of relationships with artiodactyls of the Palaeogene. The results retrieved that the superfamily was closely related to the Mixtotheriidae and Anoplotheriidae. They determined that the Cainotheriidae, Robiacinidae, Anoplotheriidae, and Mixtotheriidae formed a clade that was the sister group to the Ruminantia while Tylopoda, along with the Amphimerycidae and Xiphodontidae split earlier in the tree. [18] The phylogenetic tree published in the article and another work about the cainotherioids is outlined below: [11]
In 2022, Weppe created a phylogenetic analysis in his academic thesis regarding Palaeogene artiodactyl lineages, focusing most specifically on the endemic European families. The phylogenetic tree, according to Weppe, is the first to conduct phylogenetic affinities of all anoplotheriid genera, although not all individual species were included. He found that the Anoplotheriidae, Mixtotheriidae, and Cainotherioidea form a clade based on synapomorphic dental traits (traits thought to have originated from their most recent common ancestor). The result, Weppe mentioned, matches up with previous phylogenetic analyses on the Cainotherioidea with other endemic European Palaeogene artiodactyls that support the families as a clade. As a result, he argued that the proposed superfamily Anoplotherioidea, composed of the Anoplotheriidae and Xiphodontidae as proposed by Alan W. Gentry and Hooker in 1988, is invalid due to the polyphyly of the lineages in the phylogenetic analysis. However, the Xiphodontidae was still found to compose part of a wider clade with the three other groups. [16] He also proposed that Leptotheridium, previously relocated from the "Dacrytheriidae" to the Xiphodontidae, composes part of a paraphyletic anoplotheriid clade with the dacrytheriines Catodontherium and Dacrytherium. [19] [8] [16]
The dacrytheriines share the presences of preorbital fossae, distinguishing them cranially from anoplotheriines. [20] C. buxgovianum is known by a preorbital fossa similar to Dacrytherium, but its development is less marked. [21] C. buxgovianum and C. fallax are known by fragmentary cranial fossil remains, described by Stehlin in 1910 and stored currently at the Natural History Museum of Basel. The compressed skull fragment specimen Ef.419, belonging to C. buxgovianum, is a back portion of the facial skull with the moderate-sized right orbit located slightly above the edge of the alveolar process. The infraorbital foramen is somewhat distant from the front of the orbit, is above the M1 tooth, and differs in position to that of Dacrytherium. Stehlin speculated that the top view of the skull of Catodontherium may have been similar in appearance to that of Dacrytherium. [6] C. fallax, known by three skull fragments, has a similar texture to that observed in C. buxgovianum. Its infraorbital foramen is above the border of M2 and M1, a depression occurring at the middle position of where M2 is. [6]
The horizontal ramus of the mandible of C. buxgovianum is large and has less of a proportion increase in the back area compared to that of Dacrytherium ovinum. [6]
The dental formula of Catodontherium and other anoplotheriids is 3.1.4.33.1.4.3 for a total of 44 teeth, consistent with the primitive dental formula for early-middle Palaeogene placental mammals. [22] [23] Anoplotheriids have selenodont or bunoselenodont premolars and molars made for folivorous/browsing diets, consistent with environment trends in the late Eocene of Europe. The canines of the Anoplotheriidae are premolariform in shape, meaning that the canines are overall undifferentiated from other teeth like incisors. The lower premolars of the family are piercing and elongated. The upper molars are bunoselenodont in form while the lower molars have selenodont labial cuspids and bunodont lingual cuspids. The subfamily Dacrytheriinae differs from the Anoplotheriinae based on the presence of a third cusp between the metaconid and entoconid of the lower molars and having molariform premolars with crescent-shaped paraconules. [10]
Catodontherium is diagnosed as having more elongated lower premolars, except for the P4, compared to Dacrytherium and lower molars without the side mediostylid cusp that Dacrytherium has. The third lobe (or division) of the M3 has a double-cusped formation. The upper molars are trapezoidal in outline, with the labial sides of their paracone and metacone cusps being slightly ridged. [8] The molars are very brachydont while the last two back premolars are sharp. [20] The molars of C. argentonicum? are seemingly more bunodont compared to other species of Catodontherium and Dacrytherium. [8]
Catodontherium is known by very few postcranial remains, leading Hooker to state in 2007 that the genus lacks any astragalus fossil designated to it. [17] Alternatively in 1947, Jean Viret and J. Prudant described proximal ends of the radii bones that had typical anoplotheriid morphologies that correspond to unusual forelimb movement compared to other artiodactyls. They designated one proximal radius end to C. robiacense on the basis that it was transversely enlarged and was primitive in appearance compared to that of Dacrytherium because it was not as differentiated anatomically. They also said the astragalus of Catodontherium has similar sizes and proportions to that of "Brachyodus borbonicus" (= Elomeryx borbonicus) but differs by a projection on its external face near a facet joint for the calcaneum. [24] According to Jean Sudre in 1969, C. robiacense has tridactyl (three-toed) hind legs, citing from a 1948 source by A. Favre that there is no trace of the 1st and 5th metatarsals. [21]
For much of the Eocene, a hothouse climate with humid, tropical environments with consistently high precipitations prevailed. Modern mammalian orders including the Perissodactyla, Artiodactyla, and Primates (or the suborder Euprimates) appeared already by the early Eocene, diversifying rapidly and developing dentitions specialized for folivory. The omnivorous forms mostly either switched to folivorous diets or went extinct by the middle Eocene (47 – 37 Ma) along with the archaic "condylarths". By the late Eocene (approx. 37 – 33 Ma), most of the ungulate form dentitions shifted from bunodont cusps to cutting ridges (i.e. lophs) for folivorous diets. [25] [26]
Land-based connections to the north of the developing Atlantic Ocean were interrupted around 53 Ma, meaning that North America and Greenland were no longer well-connected to Western Europe. From the early Eocene up until the Grande Coupure extinction event (56 Ma – 33.9 Ma), the western Eurasian continent was separated into three landmasses, the former two of which were isolated by seaways: Western Europe (an archipelago), Balkanatolia, and eastern Eurasia (Balkanatolia was in between the Paratethys Sea of the north and the Neotethys Ocean of the south). [9] The Holarctic mammalian faunas of Western Europe were therefore mostly isolated from all other regions, allowing for endemism to occur within Western Europe. [26] The European mammals of the late Eocene (MP17 – MP20) were mostly descendants of endemic middle Eocene groups as a result. [27]
C. argentonicum? was present in Western Europe by MP11 based on fossil presence at the locality of Argenton in France. [8] [13] In terms of undisputed species, C. fallax made an appearance in the continent by MP14 based on its presence at the locality of Egerkingen, Switzerland. [28] By MP14, it would have coexisted with perissodactyls (Palaeotheriidae, Lophiodontidae, and Hyrachyidae), non-endemic artiodactyls (Dichobunidae and Tapirulidae), endemic European artiodactyls (Choeropotamidae, Cebochoeridae, Mixtotheriidae, Amphimerycidae, Xiphodontidae, and other members of Anoplotheriidae), and primates (Adapidae). [29] [14] [30] The stratigraphic ranges of Catodontherium also overlapped with metatherians (Herpetotheriidae), cimolestans (Pantolestidae, Paroxyclaenidae), rodents (Ischyromyidae, Theridomyoidea, Gliridae), eulipotyphlans, bats, apatotherians, carnivoraformes (Miacidae), and hyaenodonts (Hyainailourinae, Proviverrinae). [28] Other MP13-MP14 sites have also yielded fossils of turtles and crocodylomorphs. [31] Catodontherium made its latest known appearance by MP16 as the species C. robiacense as indicated by the French locality of Robiac, still having coexisted with largely similar faunas. [28] [32] [13]
Artiodactyls are placental mammals belonging to the order Artiodactyla. Typically, they are ungulates which bear weight equally on two of their five toes. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two orders is that many artiodactyls digest plant cellulose in one or more stomach chambers rather than in their intestine. Molecular biology, along with new fossil discoveries, has found that cetaceans fall within this taxonomic branch, being most closely related to hippopotamuses. Some modern taxonomists thus apply the name Cetartiodactyla to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use "even-toed ungulates" to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature.
Palaeotherium is an extinct genus of equoid that lived in Europe and possibly the Middle East from the Middle Eocene to the Early Oligocene. It is the type genus of the Palaeotheriidae, a group exclusive to the Palaeogene that was closest in relation to the Equidae, which contains horses plus their closest relatives and ancestors. Fossils of Palaeotherium were first described in 1782 by the French naturalist Robert de Lamanon and then closely studied by another French naturalist, Georges Cuvier, after 1798. Cuvier erected the genus in 1804 and recognized multiple species based on overall fossil sizes and forms. As one of the first fossil genera to be recognized with official taxonomic authority, it is recognized as an important milestone within the field of palaeontology. The research by early naturalists on Palaeotherium contributed to the developing ideas of evolution, extinction, and succession and demonstrating the morphological diversity of different species within one genus.
Anoplotherium is the type genus of the extinct Palaeogene artiodactyl family Anoplotheriidae, which was endemic to Western Europe. It lived from the late Eocene to the earliest Oligocene. It was the fifth fossil mammal genus to be described with official taxonomic authority, with a history extending back to 1804 when its fossils from Montmartre in Paris, France were first described by the French naturalist Georges Cuvier. Discoveries of incomplete skeletons of A. commune in 1807 led Cuvier to thoroughly describe unusual features for which there are no modern analogues. His drawn skeletal and muscle reconstructions of A. commune in 1812 were amongst the first instances of anatomical reconstructions based on fossil evidence. Cuvier's contributions to palaeontology based on his works on the genus were revolutionary for the field, not only proving the developing ideas of extinction and ecological succession but also paving the way for subfields such as palaeoneurology. Today, there are four known species.
Xiphodontidae is an extinct family of herbivorous even-toed ungulates, endemic to Europe during the Eocene 40.4—33.9 million years ago, existing for about 7.5 million years. Paraxiphodon suggests that they survived into the Lower Oligocene, at least.
Anoplotheriidae is an extinct family of artiodactyl ungulates. They were endemic to Europe during the Eocene and Oligocene epochs about 44—30 million years ago. Its name is derived from the Ancient Greek: ἂνοπλος ("unarmed") and θήριον ("beast"), translating as "unarmed beast".
Duerotherium is an extinct genus of Palaeogene artiodactyls known only from the Iberian Peninsula during the Middle Eocene, which contains one species D. sudrei. It, like other members of the Anoplotheriidae, was endemic to Western Europe. The anoplotheriine was described from a left fragment of a maxilla from the Mazaterón Formation of the Duero Basin in 2009. Its dentition is mostly typical of the Anoplotheriinae but differs by an elongated plus triangular 3rd upper premolar and very specific traits of the molars. It is thought to have been part of an endemic faunal assemblage that evolved within the Iberian Peninsula by the Middle Eocene, where climates were subtropical.
Agriochoerus is an extinct genus of scansorial herbivore of the tylopod family Agriochoeridae, endemic to North America. Agriochoerus and other agriochoerids possessed claws, which is rare within Artiodactyla, as well as likely being scansorial. Agriochoerus was first described in 1869.
Xiphodon is the type genus of the extinct Palaeogene artiodactyl family Xiphodontidae. It, like other xiphodonts, was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. Fossils from Montmartre in Paris, France that belonged to X. gracilis were first described by the French naturalist Georges Cuvier in 1804. Although he assigned the species to Anoplotherium, he recognized that it differed from A. commune by its dentition and limb bones, later moving it to its own subgenus in 1822. Xiphodon was promoted to genus rank by other naturalists in later decades. It is today defined by the type species X. gracilis and two other species, X. castrensis and X. intermedium.
Plagiolophus is an extinct genus of equoids belonging to the family Palaeotheriidae. It lived in Europe from the middle Oligocene to the early Oligocene. The type species P. minor was initially described by the French naturalist Georges Cuvier in 1804 based on postcranial material including a now-lost skeleton originally from the Paris Basin. It was classified to Palaeotherium the same year but was reclassified to the subgenus Plagiolophus, named by Auguste Pomel in 1847. Plagiolophus was promoted to genus rank by subsequent palaeontologists and today includes as many as seventeen species. As proposed by the French palaeontologist Jean A. Remy in 2004, it is defined by three subgenera: Plagiolophus, Paloplotherium, and Fraasiolophus.
Cainotheriidae is an extinct family of artiodactyls known from the Late Eocene to Middle Miocene of Europe. They are mostly found preserved in karstic deposits.
Microbunodon was a genus of extinct artiodactyl mammals in the family Anthracotheriidae. It lived between the upper Eocene and the lower Pliocene. Its fossil remains have been found in Europe and Asia.
Dichodon is an extinct genus of Palaeogene artiodactyls belonging to the family Xiphodontidae. It was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. The genus was first erected by the British naturalist Richard Owen in 1848 based on dental remains from the fossil beds in Hordle, England. He noticed similar dentitions to contemporary artiodactyls like those of the Anoplotheriidae and Dichobunidae and references the name of the genus Dichobune. Eventually, it was found to be more closely related to Xiphodon and now includes 11 species, although one of them may be synonymous.
The research history of Anoplotherium spans back to 1804 when Georges Cuvier first described the fossils of this extinct artiodactyl and named the genus after describing Palaeotherium, making it one of the first fossil mammal genera to be described as well as having one of the earliest official taxonomic authorities. It was also amongst the first fossil genera to be reconstructed by drawings and biomechanics. Subsequent descriptions of fossil evidence by Cuvier are also said to have been some of the earliest instances of palaeoneurology and palaeopathology. Anoplotherium was a significant find in palaeontological history and was once an iconic element of text and classroom sources of palaeontology, geology, and natural history. Today, it has a lessened cultural status compared to the 19th century as a result of public interest in Mesozoic dinosaurs or Neogene-Quaternary mammals, but it is still regularly acknowledged in sources of the history of palaeontology.
Diplobune is an extinct genus of Palaeogene artiodactyls belonging to the family Anoplotheriidae. It was endemic to Europe and lived from the late Eocene to the early Oligocene. The genus was first erected as a subgenus of Dichobune by Ludwig Rütimeyer in 1862 based on his hypothesis of the taxon being a transitional form between "Anoplotherium" secundaria, previously erected by Georges Cuvier in 1822, and Dichobune. He based the genus etymology off of the two-pointed pillarlike shapes of the lower molars, which had since been a diagnosis of it. However, in 1870, Diplobune was elevated to genus rank by Oscar Fraas, who recognized that Diplobune was a distinct genus related to Anoplotherium and not Dichobune. After several revisions of the anoplotheriids, there are currently four known species of which D. minor is the type species.
Dacrytherium is an extinct genus of Palaeogene artiodactyls belonging to the family Anoplotheriidae. It occurred from the Middle to Late Eocene of Western Europe and is the type genus of the subfamily Dacrytheriinae, the older of the two anoplotheriid subfamilies. Dacrytherium was first erected in 1876 by the French palaeontologist Henri Filhol, who recognised in his studies that it had dentition similar to the anoplotheriids Anoplotherium and Diplobune but differed from them by a deep preorbital fossa and a lacrimal fossa, the latter of which is where the genus name derives from. D. ovinum, originally classified in Dichobune, is the type species of Dacrytherium. Henri Filhol named D. elegans in 1884, and Hans Georg Stehlin named the species D. priscum and D. saturnini in 1910.
Ephelcomenus is an extinct genus of Palaeogene artiodactyls endemic to Western Europe. It contains one species E. filholi, which was first described by Richard Lydekker in 1889 but eventually classified to its own genus by the Swiss palaeontologist Johannes Hürzeler in 1938. It has an uncertain stratigraphic range, but some sources suggest that it was present in the Oligocene after the Grande Coupure turnover event of western Europe.
Robiatherium is an extinct genus of Palaeogene artiodactyls containing one species R. cournovense. The genus name derives from the locality of Robiac in France where some of its fossil were described plus the Greek θήρ/therium meaning "beast" or "wild animal". It was known only from the middle Eocene and, like other anoplotheriids, was endemic to Western Europe. The genus was erected by Jean Sudre in 1988 for a species originally attributed to the xiphodont genus Paraxiphodon in 1978. Robiatherium had dentitions typical of the subfamily Anoplotheriinae, differing from other genera by specific differences in the molars. It is one of the earliest-appearing anoplotheriine species in the fossil record as well as the earliest to have appeared in Central Europe.
Mixtotherium is an extinct genus of Palaeogene artiodactyls belonging to the monotypic family Mixtotheriidae. Known informally as mixtotheriids or mixtotheres, these artiodactyls were endemic to western Europe and occurred from the middle to late Eocene. The genus and type species were both first established by the French naturalist Henri Filhol in 1880. Several species are well known by good skull fossils, which were informative enough to allow for classifications of the species to their own family. The Mixtotheriidae, first recognized by Helga Sharpe Pearson in 1927, is currently known by 7 valid species, although M. priscum is thought by several authors to be synonymous with M. gresslyi. The affinities of the Mixtotheriidae in relation to other artiodactyl families is uncertain, but it is currently thought to have been related to the Cainotherioidea and Anoplotheriidae.
Haplomeryx is an extinct genus of Palaeogene artiodactyls belonging to the family Xiphodontidae. It was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. Haplomeryx was first established as a genus by the German naturalist Max Schlosser in 1886 based on a molar tooth set from Quercy Phosphorites deposits. Three additional species were erected and classified to the xiphodontid genus while one other species, first recognized in 1822, was tentatively classified to it and remains unresolved in affinity.
Amphimeryx is an extinct genus of Palaeogene artiodactyls belonging to the family Amphimerycidae that was endemic to the central region of western Europe and lived from the Late Eocene to the Early Oligocene. It was erected in 1848 by the French palaeontologist Auguste Pomel, who argued that its dentition was roughly similar to those of ruminants. Hence, the etymology of the genus name means "near ruminant," of which it derives from the ancient Greek words ἀμφί (near) and μήρυξ (ruminant). The type species A. murinus was previously recognized as a species of Dichobune by the French palaeontologist Georges Cuvier in 1822 before its eventual reclassification to its own genus. Two other species A. collotarsus and A. riparius are recognized also today although the former may be synonymous with A. murinus while the latter is known solely by a now-lost fossil specimen.